The water has been the focus of the search since Avonte vanished, but an army of cops has been dispatched to scour the city, including the subway tunnels — based on his affinity for trains — in case they were wrong.

Police also brought in a "drift expert" who helped calculate tides, sources said. The search has been difficult because the water is extremely murky with visibility at various points down to as little as three inches, sources said.

Sources say police have spoken at length with autism experts about the case, who told them that some autistic children are fascinated with water but lack the ability to fully understand its dangers, like depths and currents. Many have minimal, if any, swimming skills, the advisers said.

"For reasons not entirely clear, missing children with autism, especially those who are severely affected, have a tendency to wander or elope from a safe environment and will often seek bodies of water such as streams, ponds, lakes, rivers, creeks, storm-water retention/detention basins, and backyard and public swimming pools," the guide says.

It also said that between 2009 and 2011, 91 percent of deaths for autistic children 14 and younger after going missing are attributable to accidental drowning.

Avonte's father, however, told CNN that his son did not have an attraction to water.

The 14-year-old, who cannot speak, was last seen on surveillance video leaving his school at 1-50 51st Ave. on Oct. 4.

Questions have been raised about the school's response on that day. According to a $25 million notice of claim, the first step to suing the city, Avonte walked past a school safety agent and out the door.

Despite being told about the boy's disappearance two minutes after he left, the principal did not call 911 for nearly an hour afterward, police sources said.

Sources said that the principal and other school officials believed that he was still inside the school. Police Commissioner Raymond Kelly said he did not believe the guard was at fault.

In the more than two weeks since, police have scoured the city for the Rego Park teen, dispatching helicopters, boats and K-9 units. Officers have searched subway tunnels, based on Avonte's affinity for trains, and hundreds of volunteers have canvassed the city with fliers.

"We are doing feasibly everything we can do," Kelly said Monday, including interviewing "virtually everyone" who is on the sex offender registry for abusing a child under the age of 16.

Police have urged anyone who thinks they may have seen Avonte to call the police immediately. He was last seen wearing a gray striped shirt, black jeans and black sneakers. He is 5-foot-3 and weighs 125 pounds.

Anyone with information is asked to call the NYPD's Crime Stoppers Hotline at 800-577-TIPS. The public can also submit tips by logging onto the Crime Stoppers website at www.nypdcrimestoppers.com or by texting their tips to 274637(CRIMES), then entering TIP577.

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